feat(admin): allow a guarded key-rotation run

Add an optional admin-triggered key rotation on pg-boss that re-encrypts
the whole encrypted-column corpus to the active key, reusing the same
column registry as the command-line tool (which stays the canonical path).
POST /api/admin/encryption/rotate enqueues a singleton run and is gated by
cookie-only admin plus a fresh second factor. The run is idempotent
(rows already on the active key are skipped), active-key-only, and never
adds or drops a key — the env key map stays operator-owned, so a key drop
remains a deliberate redeploy. It fails closed per row and reports totals
into the audit trail the status view reads.

src/app/api/admin/encryption/rotate/route.ts

@@ -0,0 +1,73 @@
+/**
+ * POST /api/admin/encryption/rotate
+ *
+ * v1.23 — admin-triggered encryption-key rotation. Enqueues the
+ * `encryption-key-rotate` pg-boss job, which re-encrypts the whole encrypted-
+ * column corpus to the configured ACTIVE key id. The CLI
+ * (`scripts/rotate-encryption-key.ts`) stays the canonical path; this is a
+ * convenience that reuses the same column registry and is safe by construction:
+ *
+ *  - ACTIVE-KEY-ONLY + NEVER ADDS / DROPS A KEY: the job only writes the active
+ *    key and never touches `ENCRYPTION_KEYS`. Dropping a key remains an env +
+ *    redeploy act.
+ *  - IDEMPOTENT: rows already on the active key are skipped; the singleton key
+ *    coalesces duplicate triggers into one queued run.
+ *
+ * Auth: cookie-only `requireAdmin` (Bearer can never reach admin) PLUS
+ * `requireFreshMfa` step-up — re-encrypting the whole sensitive corpus is a
+ * high-blast-radius action. An admin without a second factor cannot use the
+ * button and falls back to the CLI (this is intentional: step-up cannot be
+ * softened, and the CLI is the documented canonical path).
+ */
+import {
+  apiHandler,
+  requireAdmin,
+  requireFreshMfa,
+  MFA_STEP_UP_MAX_AGE_SECONDS,
+} from "@/lib/api-handler";
+import { apiError, apiSuccess, getClientIp } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { auditLog } from "@/lib/auth/audit";
+import { getGlobalBoss } from "@/lib/jobs/boss-instance";
+import {
+  ENCRYPTION_KEY_ROTATE_QUEUE,
+  ENCRYPTION_KEY_ROTATE_SINGLETON,
+} from "@/lib/jobs/encryption-key-rotate";
+import { getActiveKeyId } from "@/lib/crypto";
+import { NextRequest } from "next/server";
+
+export const POST = apiHandler(async (request: NextRequest) => {
+  // Cookie-only admin, then a fresh second factor. Both resolution paths are
+  // cookie-only, so a Bearer token cannot reach either.
+  await requireAdmin();
+  const { user } = await requireFreshMfa(MFA_STEP_UP_MAX_AGE_SECONDS);
+  annotate({ action: { name: "admin.encryption.rotate.requested" } });
+
+  const boss = getGlobalBoss();
+  if (!boss) {
+    return apiError("Background worker is not available", 503);
+  }
+
+  const jobId = await boss.send(
+    ENCRYPTION_KEY_ROTATE_QUEUE,
+    { requestedByUserId: user.id, enqueuedAt: new Date().toISOString() },
+    {
+      // Coalesce duplicate triggers: at most one queued run at a time.
+      singletonKey: ENCRYPTION_KEY_ROTATE_SINGLETON,
+      retryLimit: 2,
+      retryDelay: 60,
+    },
+  );
+
+  await auditLog("admin.encryption.rotate.requested", {
+    userId: user.id,
+    ipAddress: getClientIp(request),
+    details: { activeKeyId: getActiveKeyId(), enqueued: Boolean(jobId) },
+  });
+
+  annotate({ meta: { rotate_enqueued: Boolean(jobId) } });
+
+  // A null jobId means the singleton coalesced this trigger onto an already-
+  // queued run — still "accepted" from the operator's point of view.
+  return apiSuccess({ accepted: true, alreadyQueued: !jobId });
+});